The present invention relates to mechanical power transmissions which provide continuously variable torque and speed ratios. More specifically, it relates to transmissions that employ motors and generators coupled with planetary gearing to generate variable speeds.
Conventional transmissions used on large diesel trucks typically require a large number of gears for optimum engine performance. This is because diesel engines, unlike gasoline engines, generally operate most effectively within a narrow speed range. As a result, large trucks can increment their speeds by only a small amount in any given gear, making it necessary to employ large numbers of gears to cover the full speed range of the vehicle. It is not uncommon, for example, to find trucks that have 9, 13, or 18 gear ratios.
An ideal transmission would have an infinite number of "gear" ratios to allow the speed of the output shaft to vary while the input remains constant. Such a device is referred to as a continuously variable transmission, or CVT. Some CVT's use belts wrapped around variable diameter pulleys for providing variable speed and torque ratios, while others use fluids or other power transmission elements. Most CVT's, however, are not rugged enough for handling large quantities of torque and power, and many will show signs of wear after prolonged usage. By contrast, this invention provides a continuously variable transmission that is relatively simple in construction and extremely rugged for heavy-duty usage. Furthermore, only a few gear ratios are necessary for attaining maximum speed, in fact far fewer gears than would be required in a comparable standard transmission.
On trucks and buses it is often necessary to brake the vehicle over long downgrades or repeated stops and starts without placing excessive wear on the service brakes. On automatic transmissions, speed retardation is achieved by means of the fluid coupling which converts the kinetic energy into heat. With standard transmissions, an engine compression brake is often used that converts the engine into a power-consuming air compressor. When this brake is used with a conventional transmission, the driver is required to change gears as the vehicle decelerates to maintain an optimum engine speed. The present invention, when used in conjunction with such a compression brake, removes this burden from the driver, since the driver is not required to shift gears to keep the engine brake operating at the proper speed; the transmission can automatically maintain a constant engine speed even as the vehicle accelerates or decelerates during braking, and it can also shift automatically when required.
It is well known that any type of CVT unit can be combined with a differential gear mechanism to reduce the full power load that would otherwise have to be handled entirely by the CVT. It is further known that a motor and generator can operate collectively as a CVT unit. Examples of this concept abound in the patent literature and can be found in the references cited. One of the earliest inventions which discloses the idea for combining motors and generators as CVT's in conjunction with planetary gearing can be found in U.S. Pat. No. 1,515,321 issued in 1924. Numerous elaborations on this idea have appeared in the patent literature since that time, and new embodiments of the same concept continue to be patented on a regular basis. Despite all these patents, however, there are still no transmissions in commercial production employing the split-power principle embodied in these inventions. Most of these inventions lack the specificity that is required to build an actual working transmission. Furthermore, these inventions may work well in theory using ideal elements but may not work efficiently using real components operating at high speeds and with stressful loads.
Accordingly, the general object of the invention is to provide a novel design, arrangement and integration of parts for a significantly improved transmission system. Part of the general object is also to provide a complete disclosure of the invention through detailed drawings, descriptions, and extensive mathematical analysis.
Another object of the invention is to provide a transmission which does not require a mechanical clutch and which is extremely simple to operate.
A further object of the invention is to provide a transmission which has an integral speed retarder and which can operate with an external (engine) retarder if necessary.
The present invention, which is the culmination of thousands of hours of research and development, is highly specific in its claims. The claims are limited to certain factors which include, among other things, the design parameters of the motor-generator units. For example, the invention requires that the outer diameters of the motor-generators be larger than their widths, which is uncommon for a typical D.C. motor. The invention also qualifies these motor-generators by requiring that they be of the permanent magnet type. Even further, the claims require that the rotors carry the permanent magnets and that the stators carry the windings, which is the reverse of the conventional D.C. motor. Of course, all these restrictions make it possible for any manufacturer to circumvent the patent merely by changing just one of these design parameters. However, these design specifications are essential to the technological and commercial viability of the present invention.